It is well known that it is highly desirable to operate an internal combustion engine with the highest possible compression ratio.
It is also well known that the practical limit of such compression ratio is determined by the explosive detonation, and/or the ignition, of the fuel employed.
One of the reasons that such detonation occurs is that at ignition time some of the fuel "cracks" into explosively oxidizing components. Thus, instead of burning (hydroxylation), the fuel may crack into solid carbon, H.sub.2, methane, etc., in which case the hydrogen will explosively oxidize.
Therefore, in order to avoid such detonation, practical internal combustion engines must operate under fairly low compression ratios which, in turn, substantially lower their efficiency.
Because of the detonation problem, even at low compression ratios, volatile fuels cannot be allowed to burn in excess air and are instead premixed in carburators or injected in intake manifolds or equivalent devices, always in the presence of limited quantities of air, thus insuring a low air-to-fuel ratio. This not only further lowers the efficiency, but also leaves substantial quantities of unburnt hydrocarbons. Consequently, such volatile fuels can only be compressed to relatively low pressures and are ignited in the combustion chamber with an electric discharge, such as that produced by the well-known spark plugs.
Heavier fuels are usually injected in the combustion chamber and since their cracking occurs at higher temperatures they may be compressed to correspondingly higher values. Nevertheless, since cracking and detonation will eventually occur, they are also compressed to a relatively low value and are ignited by a high temperature device, such as a glow-plug, glow-rod, glow-sphere, etc. To increase the efficiency and contain the detonation, fuels are sometimes injected and burned in precombustion chambers and similar or equivalent devices.
Heavy fuels, such as diesel fuel, are difficult to ignite. Therefore they are almost always injected as a fine mist, the reasoning being that the finer the mist, the larger the total surface of contact between fuel and air and therefore the easier the ignition and the better the combustion.
Thus, while high compression ratios are desirable, while self-ignition is also desirable, and while combustion in excess air is again desirable, none of these objectives can be practically realized according to prior art.